ABSTRACT Tuberculosis (TB) is a priority disease for the World Health Organization (WHO), and the emergence of multidrug-resistant Mycobacterium tuberculosis (Mtb) isolates poses an enormous threat to TB intervention efforts. South Africa has a rich history of medicinal plant use for treatment of respiratory ailments and infections, as well as HIV. Amongst the traditional and complementary medicines (T/CAM), Sutherlandia frutescens (SF) is commonly used to alleviate respiratory and HIV-associated conditions/ailments. Recent analysis of an NIH-sponsored clinical trial of the safety of SF consumption by HIV+ individuals suggests that SF may reduce the bactericidal effects of first-line isoniazid (INH) therapy for TB, which could contribute to TB transmission and the emergence of multidrug- resistant (MDR) Mtb bacilli. The revision application submitted here will explore the potential for SF to hinder INH bactericidal efficacy. Specifically, it will investigate the capacity of SF to inhibit intracellular effector molecules, including nitric oxide and reactive oxygen species, and to alter the mycobacterial SOS response. In addition, it will address the potential for SF to block INH killing of Mtb in culture and to block INH killing of Mtb in an aerosol infection humanized mouse model. Outcomes will focus on SF-dependent effects on INH efficacy and comparative organ pathology during treatment. Consistent with the research aims of the parent grant (U01HD085531), the study will apply a combination of mycobacterial reporter mutants and advanced florescence microscopy to investigate the role of SOS- dependent mutagenesis in Mtb exposed to INH and SF as a key molecular mechanism driving the emergence of MDR-TB. In summary, the project aims to address a long-standing question among practicing South African and international infectious disease clinicians and health policy makers around the impact of T/CAMs on the efficacy of frontline anti-TB chemotherapy. To this end, it combines a strong scientific rationale with a collaborative team comprising South African and U.S. researchers with the necessary expertise. As such, the project responds directly to the FOA in ensuring support for relevant scientific research led by SA investigators from underrepresented backgrounds, and conducted at research facilities in South Africa which are proximal to the disease.